1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a liquid crystal display (LCD) device having a wide viewing angle and an array substrate for the same.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device utilizes an optical anisotropy and birefringence properties of liquid crystal molecules to display images. The liquid crystal display (LCD) device usually has first and second substrates spaced apart from and opposing each other. The first and second substrates respectively have electrodes for forming an electric field between the electrodes. That is, if voltage is applied to the electrodes of the liquid crystal display (LCD) device, an electric field is formed between the electrodes and the electric field changes alignments of the liquid crystal molecules. The changed alignments of the liquid crystal molecules control a light transmittance through the liquid crystal and thus images can be displayed by controlling the light transmittance through the liquid crystal.
FIG. 1 is an exploded perspective view of a related art liquid crystal display (LCD) device. In FIG. 1, a liquid crystal display (LCD) device 11 has an upper substrate 5 having a black matrix 6, a color filter layer 8, and a common electrode 18 on the color filter layer 8, and a lower substrate 22 having a thin film transistor T and a pixel electrode 17 connected to the thin film transistor T. The color filter layer 8 has sub-color filters of red (R), green (G) and blue (B), and the black matrix 6 is formed between the sub-color filters. A plurality of pixel regions P is defined on the lower substrate 22 and array lines are formed around the pixel region P. Liquid crystal 14 is interposed between the upper and lower substrates 5 and 22. A gate line 13 is formed in a first direction and a data line 15 is formed in a second direction perpendicular to the first direction. The gate and data lines 13 and 15 define the pixel region P by crossing each other and the thin film transistor T is formed near crossing portion of the gate and data lines 13 and 15. The thin film transistors “T” are formed in a matrix form on the lower substrate 22, i.e., an array substrate. The pixel electrode 17 is formed of transparent conductive metal material such as indium tin oxide (ITO) in the pixel region “P. A storage capacitor C connected to the pixel electrode 17 in parallel is formed over the gate line 13. A portion of the gate line 13 serves as a first storage electrode and a metal layer formed of the same material as source and drain electrodes serves as a second storage electrode. The metal layer contacts the pixel electrode 17 to receive a signal from the pixel electrode 17. Because liquid crystal molecules are aligned by an electric field formed between the common and pixel electrodes 18 and 17, the liquid crystal display (LCD) device (specially TN (twisted nematic) mode liquid crystal display (LCD) device) has a narrow viewing angle. To overcome the aforementioned problem, a method to improve a viewing angle by dividing the pixel region into many domains, in which the liquid crystal molecules in one of the domains have a symmetric orientation to the orientation of the liquid crystal molecules in a next domain, has been suggested. A structure of the liquid crystal display (LCD) device to improve the viewing angle will be described hereinafter with reference to FIG. 2.
FIG. 2 is a plan view of a related art liquid crystal display (LCD) device having a multi-domain structure. In FIG. 2, a gate line 52 is formed in a first direction on a substrate 50, which may be a lower substrate of the LCD device, and a data line 54 crossing the gate line 52 is formed in a second direction. The gate line 52 and the data line 54 define a pixel region P. At the crossing the gate line 52 and the data line 54, a thin film transistor T having a gate electrode 56, an active layer 58, a source electrode 60 and a drain electrode 62 is formed. A pixel electrode 64 connected to the drain electrode 62 is formed in the pixel region P, and the pixel electrode 64 includes a slit S, which is formed by removing the pixel electrode 64 along a diagonal of the pixel electrode 64 and divides the pixel region P into two parts. A sub-electrode 66 is formed corresponding to the slit S.
Meanwhile, an organic pattern 80 is formed in a peripheral area of the pixel region P, and the organic pattern 80 is disposed on an upper substrate (not shown), which includes a common electrode (not shown).
Here, the organic pattern 80 and the slit S distort electric field perpendicularly induced between the pixel electrode 64 and the common electrode, and the sub electrode 66 increases distortion of the electric field. At this time, although not shown in the figure, a first alignment layer over the lower substrate 50 and a second alignment layer over the upper substrate are rubbed such that rubbing directions of the alignment layers are at 90 degrees to each other, wherein the rubbing direction of the first alignment layer is at 45 degrees to the data line 54.
Therefore, in the related art LCD device, electric field is induced symmetrically with respect to the slit S, and the liquid crystal molecules are arranged along the symmetric electric field.
The liquid crystal molecules in left and right sides A1 and B1 of the pixel region P are parallel to electric field, and thus are stable. Also, the liquid crystal molecules in upper and lower sides A2 and B2 of the pixel region P are stable, though the liquid crystal molecules are arranged in the opposite direction to the liquid crystal molecules in the left and right sides A1 and B1 of the pixel region P and go away from the electric field.
In the LCD device, two domains, which are separated by the slit S and where the liquid crystal molecules are differently arranged, are formed in the pixel region P, and each domain, also, includes two areas of A1 and A2 or B1 and B2, for example. Accordingly, stability in arrangement of the liquid crystal molecules is lowered. Additionally, light leakage and residual images occur due to the low arranging stability of the liquid crystal molecules, and spots happen when the LCD device is touched by weak force.